Itraconazole, a well-known antifungal agent, is defined in the USAN and USP Dictionary of Drug Names as 4-[4-[4-[4-[[2-(2,4-dichlorophenyl)-2-(1H-1,2,4-triazol-1-ylmethyl)- 1,3-dioxolan-4-yl]methoxy]phenyl]-1-piperazinyl]phenyl]-2,4-dihydro-2-(1-m ethylpropyl)-3H-1,2,4-triazol-3-one or alternatively as (.+-.)-1-sec-butyl-4-[p-[4-[p-[[(2R*,4S*)-2-(2,4-dichlorophenyl)-2-(1H-1,2 ,4-triazol-1-ylmethyl)-1,3-dioxolan-4-yl]methoxy]phenyl]-1-piperazinyl]phen yl]-.DELTA..sup.2 -1,2,4-triazolin-5-one. The commercially available material is the cis isomer in the dioxolane ring and is represented by the structural formula I: ##STR1##
It will be noted that there are three asymmetric carbons in formula I (denoted by asterisks): two in the dioxolane ring and one in the sec-butyl side chain on the triazolone. There are eight possible isomers of a structure having three asymmetric carbons: (R,R,R), (R,R,S), (R,S,S), (S,S,S), (R,S,R), (S,R,S), (S,R,R) and (S,S,R). Because the commercially available itraconazole is a cis isomer, it comprises a mixture of only those isomers that describe a cis relationship in the dioxolane ring. Adopting the convention that the first denoted chiral center is at C-2 of the dioxolane rind, the second is at C-4 of the dioxolane and the third is in the sec-butyl group, commercial itraconazole is a mixture of (R,S,S), (R,S,R), (S,R,S) and (S,R,R) isomers. Compounds of this invention have the (2R,4S) and (2S,4R) configurations in the dioxolane ring.
The hydroxylation of the methylene carbon of the sec-butyl side chain creates an additional chiral center and gives rise to eight additional possible enantiomers. The compounds of the present invention are those in which the two asymmetric centers in the butyl chain are R (at the .alpha. carbon) and S (at the .beta. carbon). ##STR2##
The graphic representations of racemic, ambiscalemic and scalemic or enantiomerically pure compounds used herein are taken from Maehr J. Chem. Ed. 62, 114-120 (1985): solid and broken wedges are used to denote the absolute configuration of a chiral element; wavy lines indicate disavowal of any stereochemical implication which the bond it represents could generate; solid and broken bold lines are geometric descriptors indicating the relative configuration shown but denoting racemic character; and wedge outlines and dotted or broken lines denote enantiomerically pure compounds of indeterminate absolute configuration. Thus, among the structures below, those having open wedges are intended to encompass both of the pure enantiomers of that pair, those having solid wedges are intended to encompass the single, pure enantiomer having the absolute stereochemistry shown.
Itraconazole is an orally active, broad-spectrum anti-fungal agent and is structurally related to miconazole and clotrimazole. It impairs the synthesis of ergosterol, which is the principal sterol of fungal cell membranes. This presumably results in an increased permeability and leakage of intracellular content. At high concentration, cellular internal organelles involute, peroxisomes increase, and necrotic changes occur.
Following oral administration, itraconazole is slowly absorbed. Peak plasma levels are attained after 15 days of daily administration, and the pharmacokinetic behavior of itraconazole is nonlinear. The compound is eventually metabolized through the biologically active hydroxyitraconazole to several inactive metabolites. Metabolism is apparently through hepatic mechanisms, and in most subjects no metabolites are excreted in the urine [see, Hardin et al., Antimicro. Agents and Chemotherapy 32, 1310-1313 (1988)].
The racemic mixture of itraconazole has been approved for use as an antifungal agent for blastomycosis and histoplasmosis. The compound is also being investigated for use in aspergillosis, coccidioidomycosis, cryptococcosis, onychomycosis, dermatophyte and candidiasis infections.
Systemic fungal diseases (systemic mycoses) are usually chronic, very slowly developing conditions induced by opportunistic causative fungi which may not normally be pathogenic. However when they enter a host compromised by HIV, ionizing irradiation, corticosteroids, immunosuppressives, etc. or by such conditions as emphysema, bronchiectasis, diabetes mellitus, leukemia, burns and the like, they may become pathogenic. Symptoms in such fungal diseases are generally not intense, and may include fever, chills, anorexia and weight loss, malaise, and depression. Fungal diseases are often confined to typical anatomic distributions, and many involve a primary focus in the lung, with more characteristic manifestations of specific fungal infections when the fungus disseminates from a primary focus. For example, coccidioidomycosis occurs in a primary form as an acute, benign, self-limiting respiratory disease, with progressive disease developing from the primary form as a chronic, often fatal infection of the skin, lymph glands, spleen and liver. Similarly, blastomycosis primarily involves the lungs, and occasionally spreads to the skin. Other infectious diseases such as candidiasis and paracoccidioidomycosis offer a different course, and depending on the etiology may exhibit several forms involving the skin, mucous membranes, lymph nodes, and internal organs.
Superficial fungal infections are caused by dermatophytes or fungi that involve the outer layers of the skin. hair or nails. The infections may result in a mild inflammation, and cause intermittent remissions and exacerbations of a gradually extending, scaling, raised lesion. Yeast infections including candidiasis, and oral candidiasis (thrush) are usually restricted to the skin, and mucous membranes, and the symptoms vary with the site of infection.
Adverse effects associated with the administration of itraconazole include hepatotoxicity and inhibition of drug metabolism in the liver, leading to numerous, clinically significant, adverse drug interactions. [See, Gascon and Dayer, Eur. J. Clin. Pharmacol. 41, 573-578 (1991) (interaction with midazolam); Honig et al. J. Clin. Pharmacol. 33, 1201-1206 (1993) (interaction with terfenadine); and Neuvonen et al. Clin. Pharmacol. Therap. 60, 54-61 (1996) (lovastatin).] Hypersensitivity reactions including urticaria and elevations in serum liver enzymes are also associated with the administration of the drug. Hepatoxicity is a less common but more serious adverse effect. Indeed, the use of oral conazoles as first line antifungals is usually discouraged because of the potentially serious consequences of the low incidence of hepatotoxicity [See,e.g., Lavrijsen et al. Lancet 340, 251-252 (1992)].
We have found evidence in our own studies in isolated guinea pig or rabbit hearts that the administration of racemic conazoles may be associated with an increased risk of cardiac arrhythmia. Arrhythmia has not been heretofore reported as a side effect of systemic itraconazole, although a particular subtype of arrhythmia, Torsades de Pointes, has been reported when racemic itraconazole was administered concurrently with terfenadine [Pohjola et al. Eur. J. Clin. Pharmacol. 45, 191-193 (1993)]. The lack of clinical reports of arrhythmia or QT anomalies may simply be a reflection of the fact that there is to date a relatively small subject population.
The relative non-polarity and insolubility of itraconazole give rise to two other drawbacks: it cannot be readily formulated in parenteral solution and it does not penetrate the blood-brain barrier. As a result, numerous therapeutic indications which require rapid achievement of efficacious blood levels or access to the CNS are beyond treatment with itraconazole. In particular, central candidiasis, which may be responsible for AIDS related dementia, cannot be treated with itraconazole.
Thus it would be particularly desirable to find a compound with the advantages of itraconazole which would not have the aforementioned disadvantages.